Many monomers and monomeric mixtures capable of forming polymeric precipitates are known as well as the preparation of their polymeric products by reacting the monomers in aqueous or organic liquid media or in a Redox system. However, these processes, as described in the prior art, have many disadvantages and objectionable side effects among which are relatively low yields of pure polymeric product and polymers which are generally colored or subject to discoloration due to the presence of residual monomer. Also, many of these prior processes produce products in the form of gels or gummy gelatinous materials which are difficult to handle and from which the polymer is not easily isolated. Although homogeneous polymerization processes have achieved low residual monomer content, the product produced, often a flammable product solution, is gummy or highly viscous and polymeric product recovery very difficult as opposed to heterogeneous systems where the product is directly recovered as a precipitate. However, substantially all of the prior heterogeneous methods have been unable to produce a product in which the objectionable and contaminating monomeric residue is reduced to less than 0.1% (1,000 ppm). Reduction to practically exclusion of the monomer, e.g. to less than 1,000 ppm, is the desired goal of research since entrained monomeric moieties, even in small quantities, noticeably degrade polymeric properties, and in some instances, may have a carcinogenic effect which is particularly objectionable when the polymer is used in cosmetic and biological formulations. Finally, many of the prior polymerizations produce low molecular weight products since they are carried out under conditions which provide a short propagation stage resulting from the formation of a highly viscous reaction mixture thus hindering agitation and tending to terminate the reaction. In the Redox system for polymerization of acrylic acid/lactam monomers, it has been found that only certain proportions of monomer and comonomer produce commercially acceptable yields and that when the lactam is present in excess, the conversion to copolymer is less than 60%.
Accordingly, it is an object of this invention to overcome the above deficiencies by providing a commercially feasible and economical process for the precipitation polymerization of monomers.
Another object of this invention is to provide a process for producing polymer containing significantly less than 0.1 weight % residual monomer.
Still another object is to provide a commercially acceptable process for producing particulate copolymers and terpolymers from any proportion of monomeric mixtures.
Another object is to produce finally divided colorless products containing not more than 500 ppm residual monomer.
These and other objects of the invention will become apparent from the following description and disclosure.